Ammonia storage capacity of scr catalyst unit

ABSTRACT

The present disclosure describes methods for evaluating ammonia storage capacity of a close-coupled SCR unit while remaining compliant with prescribed emissions limits, methods of controlling an emission aftertreatment system including multiple SCR units and emission management systems for a vehicle including an internal combustion engine and an emission aftertreatment system that includes two or more SCR units.

BACKGROUND Technical Field

The present disclosure generally relates to engine emissions management,and more particularly, to engine NOx emissions management.

Description of the Related Art

Although diesel engines are known to be more economical to run thanspark-ignited engines, diesel engines inherently face challenges in thearea of emissions. For example, in a diesel engine, fuel is injectedduring the compression stroke, as opposed to during the intake stroke ina spark-ignited engine. As a result, a diesel engine has less time tothoroughly mix the air and fuel before ignition occurs. The consequenceis that diesel engine exhaust contains incompletely burned fuel known asparticulate matter, or “soot”. In addition to particulate matter,internal combustion engines including diesel engines produce a number ofcombustion products including hydrocarbons (“HC”), carbon monoxide(“CO”), nitrogen oxides (“NO_(x)”), and sulfur oxides (“SO_(x)”). Engineexhaust aftertreatment system can be utilized to reduce or eliminateemissions of these and other combustion products.

Conventionally, effective emissions control by an engine aftertreatmentsystem (EAS) requires temperatures of at least about 200° C. to beattained before diesel exhaust fluid (DEF) dosing may commence. However,during the EAS heat-up period under cold-start conditions (i.e., attemperatures of less than about 200° C.), the EAS is not effective atcontrolling emissions of certain combustion products to withinregulatory parameters. Increasing the availability of ammonia within anEAS, especially when engine exhaust temperatures are about 200° C. orless increases the ability of the EAS to control emissions to withinincreasingly stringent greenhouse gas and ultra-low NO_(x) regulations.

In a diesel engine, cold start emissions from the engine appear withinthe first 60 seconds after key-on. The appearance of cold startemissions occurs several minutes before a selective catalytic reduction(SCR) catalyst within an SCR bed of an EAS attains optimal temperaturefor NO_(x) reduction (e.g., at 250-450° C.). In some situations, thetotal duration of the cold start phase is about 600 seconds after key-onduring which about 30 g of engine-out NO_(x) can be generated.

Existing methods for improving emissions control during the cold startphase face challenges in meeting greenhouse gas and ultra-low NO_(x)regulations. One approach for shortening the SCR catalyst heat-up timeis to locate a combined SCR and diesel particular filter (DPF) in theform of a SCR On-Filter (SCRF) close to the engine. However, thisapproach may not be sufficient to address the challenges posed byultra-low NO_(x) emissions regulations.

Another approach is to include an additional close-coupled SCR anddiesel exhaust fluid (DEF) dosing system as close to the engine aspossible to take full advantage of the available thermal energy of theengine exhaust gas. The ability to achieve high levels of exhaust NO_(x)emissions control during cold portions of the startup phase, typicallyrequire that high levels of ammonia be stored in the SCR unit. However,as the SCR catalyst ages, the storage capacity of the catalystdecreases. Understanding the ammonia storage capacity of the SCRcatalyst is valuable for purposes of diagnosis of an EAS and forpurposes of controlling the performance of an EAS, especially during thecold start phase of an operation cycle.

BRIEF SUMMARY

In some aspects, embodiments of the present disclosure relate to methodsof evaluating ammonia storage capacity of a selective catalyticreduction (SCR) unit in an emissions aftertreatment system (EAS) of aninternal combustion engine. The method includes operating the EAS atsteady-state conditions. During the steady state operation, dieselexhaust fluid is dosed into exhaust gas from the internal combustionengine upstream of a close-coupled SCR unit. Exhaust gas, into which thediesel exhaust fluid has been dosed is flowed through the close-coupledSCR unit. According to the method, the exhaust gas from the closecoupled SCR unit is flowed through a downstream SCR unit. NOx emissionsfrom the EAS are controlled by the downstream SCR unit. Dosing of thediesel exhaust fluid into the flowing exhaust gas upstream of the closecoupled SCR unit is terminated and ammonia stored in the close coupledSCR unit is depleted. Dosing of the diesel exhaust fluid into theflowing exhaust gas upstream of the close coupled SCR unit is restartedand the close coupled SCR unit is reloaded with ammonia until it isdetermined that the close coupled SCR unit has reached a maximum ammonialoading. Upon determining the close coupled SCR unit has reached thethreshold ammonia loading, the method involves determining (1) an amountof ammonia loaded in the close-coupled SCR unit after restarting dosingof diesel exhaust fluid into the flowing exhaust gas upstream of theclose-coupled SCR unit, (2) an amount of ammonia used for NOx conversionin the close-coupled SCR unit after restarting dosing of diesel exhaustfluid into the flowing exhaust gas close-coupled of the close-coupledSCR unit and (3) an amount of ammonia oxidized in the SCR unit afterrestarting dosing of diesel exhaust fluid into the flowing exhaust gasupstream of the close-coupled SCR unit. The amount of ammonia stored inthe close coupled SCR unit is evaluated by subtracting (2) and (3) from(1).

In another aspect, embodiments in accordance with the present disclosureinclude a method of operating an EAS that includes two or more selectiveSCR units and is connected to an internal combustion engine. The methodincludes steps of evaluating ammonia storage capacity of a close coupledSCR unit while operating the EAS at steady-state conditions. During theevaluation of ammonia storage capacity of the close coupled SCR unit,NOx emissions from the EAS are controlled using a downstream SCR unit.In accordance with this method, one or more operation parameters of theEAS are adjusted based on the result of the evaluating ammonia storagecapacity of the close coupled SCR unit.

In another aspect, embodiments in accordance with the present disclosureinclude an emission management system for a vehicle including aninternal combustion engine and an EAS that includes the close coupledSCR unit and a downstream SCR unit. The emission management systemincludes at least one non-transitory processor readable storage mediumthat stores one of processor executable instructions or data and atleast one processor communicatively coupled to the at least onenon-transitory processor readable storage medium. In operation, theprocessor receives an indication of an ammonia storage capacity of theclose coupled SCR unit determine while operating the EAS at steady-statecondition. The processor's stores the received indication of an ammoniastorage capacity of the close coupled SCR unit determine while the EASoperates at steady-state conditions in the non-transitory processorreadable storage medium. The processor automatically controls theoperation of the internal combustion engine and/or the EAS, using thereceived indication of ammonia storage capacity, to control emissionsfrom the EAS to prescribed limits.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not necessarily drawn to scale, and some ofthese elements may be arbitrarily enlarged and positioned to improvedrawing legibility. Further, the particular shapes of the elements asdrawn, are not necessarily intended to convey any information regardingthe actual shape of the particular elements, and may have been solelyselected for ease of recognition in the drawings.

FIG. 1A is a schematic block diagram of an example of an emissionaftertreatment system coupled to an internal combustion engine.

FIG. 1B is a schematic block diagram of an example of an emissionaftertreatment system with a close coupled selective catalytic reductionunit coupled to an internal combustion engine.

FIG. 1C is a schematic diagram of an example of an emissionaftertreatment system with a close coupled selective catalytic reductionunit coupled to an internal combustion engine including a plurality ofsensors, according to one non-limiting illustrated embodiment.

FIG. 2 is a flow diagram of a method of evaluating an amount of ammoniastored in a close-coupled SCR unit, according to one non-limitingillustrated embodiment.

FIG. 3 is a flow diagram of a method of evaluating an amount of ammoniastored in a close-coupled SCR unit, according to one non-limitingillustrated embodiment.

FIG. 4 is a flow diagram of a method of controlling an emissionaftertreatment system that includes two or more SCR units, according toone non-limiting illustrated embodiment.

FIG. 5 illustrates a vehicle including an internal combustion engine, anemission aftertreatment system and a control system configured tocontrol components of the engine and emission aftertreament systemaccording to certain methods in accordance with embodiments describedherein.

FIG. 6 is a schematic block diagram of an emission management system inaccordance with some embodiments disclosed herein.

FIG. 7 is a plot of NOx and ammonia concentration vs time during anammonia adsorption phase in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedimplementations. However, one skilled in the relevant art will recognizethat implementations may be practiced without one or more of thesespecific details, or with other methods, components, materials, etc. Inother instances, well-known structures associated with computer systems,server computers, and/or communications networks have not been shown ordescribed in detail to avoid unnecessarily obscuring descriptions of theimplementations.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprising” is synonymous with“including,” and is inclusive or open-ended (i.e., does not excludeadditional, unrecited elements or method acts).

Reference throughout this specification to “one implementation” or “animplementation” means that a particular feature, structure orcharacteristic described in connection with the implementation isincluded in at least one implementation. Thus, the appearances of thephrases “in one implementation” or “in an implementation” in variousplaces throughout this specification are not necessarily all referringto the same implementation. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more implementations.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contextclearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theimplementations.

Terms of geometric alignment may be used herein. Any components of theembodiments that are illustrated, described, or claimed herein as beingaligned, arranged in the same direction, parallel, or having othersimilar geometric relationships with respect to one another have suchrelationships in the illustrated, described, or claimed embodiments. Inalternative embodiments, however, such components can have any of theother similar geometric properties described herein indicating alignmentwith respect to one another. Any components of the embodiments that areillustrated, described, or claimed herein as being not aligned, arrangedin different directions, not parallel, perpendicular, transverse, orhaving other similar geometric relationships with respect to oneanother, have such relationships in the illustrated, described, orclaimed embodiments. In alternative embodiments, however, suchcomponents can have any of the other similar geometric propertiesdescribed herein indicating non-alignment with respect to one another.

Various examples of suitable dimensions of components and othernumerical values may be provided herein. In the illustrated, described,and claimed embodiments, such dimensions are accurate to within standardmanufacturing tolerances unless stated otherwise. Such dimensions areexamples, however, and can be modified to produce variations of thecomponents and systems described herein. In various alternativeembodiments, such dimensions and any other specific numerical valuesprovided herein can be approximations wherein the actual numericalvalues can vary by up to 1, 2, 5, 10, 15 or more percent from thestated, approximate dimensions or other numerical values.

FIG. 1A shows a block diagram providing a brief overview of a vehiclepowertrain. The components include an internal combustion engine 20 inflow communication with one or more selected components of an emissionaftertreatment system 24 (EAS). The illustrated emission aftertreatmentsystem 24 includes an oxidation system 96 upstream of a particulatefilter 100. In the embodiment shown, the oxidation system 96 is a dieseloxidation catalyst (DOC) 96 coupled in flow communication to receive andtreat exhaust from the engine 20. The DOC 96 is preferably aflow-through device that includes either a honeycomb-like or plate-likesubstrate. The DOC substrate has a surface area that includes (e.g., iscoated with) a catalyst. The catalyst can be an oxidation catalyst,which can include a precious metal catalyst, such as platinum orpalladium, for rapid conversion of hydrocarbons, carbon monoxide, andnitric oxides in the engine exhaust gas into carbon dioxide, nitrogen,water, or NO₂.

Once the exhaust has flowed through DOC 96 it flows into the particulatefilter 100, which in the illustrated embodiment is a diesel particulatefilter (DPF) 100. The DPF 100 is utilized to capture unwanted dieselparticulate matter from the flow of exhaust gas exiting engine 20, byflowing exhaust across the walls of channels within DFP 100. The dieselparticulate matter includes sub-micron sized solid and liquid particlesfound in exhaust of a diesel fueled internal combustion engine. The DPF100 can be manufactured from a variety of materials including but notlimited to cordierite, silicon carbide, and/or other high temperatureoxide ceramics.

From DPF 100, treated exhaust gases proceed through a compartment influid communication with a diesel exhaust fluid (DEF) doser 102 for theintroduction of a reductant, such as ammonia or a urea solution into theexhaust gases. The exhaust gases and reductant then flow to a selectivecatalytic reduction (SCR) system or unit 104 which includes a catalyticcore having a selective catalytic reduction catalyst (SCR catalyst)loaded thereon. System 24 can include one or more sensors (notillustrated) associated with components of the system 24, such as one ormore temperature sensors, NO_(x) sensors, NH₃ sensors, oxygen sensors,mass flow sensors, particulate sensors, and a pressure sensors.

As discussed above, the emission aftertreatment system 24 includes aSelective Catalytic Reduction (SCR) system 104. The SCR system 104includes a selective catalytic reduction catalyst which interacts withNO_(x) gases to convert the NO_(x) gases into N₂ and water, in thepresence of an ammonia reductant. The overall reactions of NO_(x)reductions in SCR are shown below.

4NO+4NH₃+O₂→4N₂+6H₂O  (1)

6NO₂+8NH₃→7N₂+12H₂O  (2)

2NH₃+NO+NO₂→2N₂+3H₂O  (3)

Where Equation (1) represents a standard SCR reaction and Equation (3)represents a fast SCR reaction.

Referring to FIG. 1B, some EAS include a “close-coupled SCR” or“upstream SCR” 112 associated with a DEF doser 114 located upstream ofthe close-coupled SCR 112. The close-coupled SCR 112 is located closerto the engine 20 than the downstream SCR 104 (sometimes referred to asan under-body SCR) and in some embodiments as close to the engine aspossible. An example of a close-coupled SCR 104 configuration isillustrated in FIG. 1B. Such close-coupled SCR configuration employsdual DEF dosers 102 and 114 (one upstream of the close-coupled SCR 112and one upstream of the downstream SCR 104 and below the close-coupledSCR 112.

FIG. 1C illustrates an example of the EAS described above with referenceto FIG. 1B. In FIG. 1C, the same reference numbers as used in FIG. 1Bare used to identify identical features illustrated in FIG. 1C. Forexample, EAS illustrated in FIG. 1C includes first DEF doser 114,upstream SCR unit 112, diesel oxidation catalyst unit 96, dieselparticulate filter 100, second DEF doser 102 and downstream SCR unit104. In the embodiment illustrated in FIG. 1C, downstream SCR 104 isillustrated as included two bricks of substrates supporting SCRcatalyst(s). EAS illustrated in FIG. 1C further includes a plurality ofNOx sensors 116. A NOx sensor 116 a is located upstream of DEF doser114. NOx sensor 116 b is located downstream of upstream SCR 112 which isupstream of downstream SCR 104. NOx sensor 116 c is positioneddownstream of downstream SCR 104. Such NOx sensors are designed todetect concentrations of NOx in the exhaust gas; however, such NOxsensors used in EAS are often unable to differentiate between NOx in theexhaust gas and ammonia in the exhaust gas. Accordingly, signalsgenerated by the NOx sensors are an indication of the concentration oramount of NOx and ammonia in the exhaust gas the sensor isinterrogating. In the embodiment illustrated in FIG. 1C, the EASincludes a thermal input device 118, e.g., an electric heater downstreamof DEF doser 114 and upstream of SCR 112. This thermal input device isused, to introduce thermal energy into the exhaust gas, therebyincreasing the temperature of the exhaust gas flowing into the closecoupled SCR unit 112. The temperature of the exhaust gas flowing intothe close coupled SCR unit 112 can also be adjusted through theimplementation of an exhaust gas recirculation system which recirculatesa portion of the exhaust gas to the internal combustion engine.Adjusting the temperature of the exhaust gas for into the close coupledSCR unit 112 is one way to adjust the temperature of the catalyst in theSCR unit 112. While the embodiment of an EAS illustrated in FIG. 1Cincludes two SCR units 112 and 104, embodiments of the presentdisclosure include an EAS that includes more than two SCR units andmethods in accordance with embodiments of the present disclosure can bepracticed in an EAS that includes two or more SCR units.

In accordance with an embodiment of the present disclosure, ammoniastorage capacity of a close coupled SCR 112 is intrusively evaluated,i.e., during operation of an EAS including an upstream SCR 112 and whileengine 20 is operating. In accordance with embodiments of the presentdisclosure, evaluation of ammonia storage capacity of a close-coupledSCR 112 includes varying the dosing of DEF during operation the EAS andengine, preferably at steady-state conditions as described below in moredetail. Evaluating the ammonia storage capacity of an SCR 112intrusively as described herein provides a more robust indication of theamount of ammonia stored in an SCR as compared to evaluating ammoniastorage capacity based on ammonia storage capacity models. Understandingthe ammonia storage capacity of an SCR is valuable for purposes ofperforming diagnostics on the performance of the EAS and/or componentsof the EAS, e.g., the close coupled SCR 112. In other embodiments,understanding the ammonia storage capacity of the close coupled SCR 112is valuable for purposes of controlling the operation of the EAS,including components of the EAS, for example, the DEF doser 114 or theheater 118. In accordance with embodiments of the present disclosure,such intrusive evaluation of the ammonia storage capacity of the closecoupled SCR unit 112 is carried out while the downstream SCR 104maintains NOx emissions from the engine within prescribed limits.

Referring to FIG. 2, in accordance with an embodiment of the presentdisclosure, a method 248 of evaluating an ammonia storage capacity of anSCR starts at step 250. The method includes operating an internalcombustion engine in fluid communication with an EAS, such as an EASillustrated in FIG. 1C that includes a close-coupled or upstream SCR anda downstream or under-body SCR. In accordance with method 248, at step252 the EAS is operated at steady state conditions. Steady-stateconditions of the EAS include a substantially constant temperature ofthe close coupled SCR 112, a substantially constant volumetric flow ofexhaust gas through the close coupled SCR 112 a substantially constantNOx content of the exhaust gas flowing to the close coupled SCR unit112. As used herein with reference to the internal combustion engine,steady-state conditions, refers to: substantially constant RPM,substantially constant load, substantially constant exhaust gastemperature, substantially constant volumetric flow of exhaust gas andsubstantially constant NOx concentration. The steady-state conditionsare not limited to those recited above and can include other operatingconditions of the EAS and the internal combustion engine. The term“substantially constant” as used herein, refers a variance of less than15% above or below the average value of the variable during the periodin question. For example, an exhaust gas temperature would be“substantially constant” when the exhaust gas temperature is between 85%and 115% of the average temperature of the exhaust gas at the point ofmeasurement (e.g., exiting the internal combustion engine or enteringthe close coupled SCR unit) during the period in question. The term“constant” as used herein, refers to the variable in question beingwithin 5% of the average value of the variable during the period inquestion. For example, an exhaust gas temperature would be “constant”when the exhaust gas temperature is between 95% and 105% of the averagetemperature of the exhaust gas at the point of measurement (e.g.,exiting the internal combustion engine or entering the close coupled SCRunit) during the period in question.

In accordance with method 248, during operation of the EAS at steadystate conditions, at step 254, NOx emissions from the EAS are controlledto be within prescribed limits by the downstream SCR 104 in FIG. 1C.

At step 256, as described in more detail below with reference to FIG. 3,method 248 determines when upstream SCR has reached a threshold ammonialoading, e.g., a maximum ammonia loading. Upon determining that upstreamSCR has reached a threshold ammonia loading, the ammonia storagecapacity of the upstream SCR is evaluated as described below in moredetail with reference to FIG. 3. The method illustrated in FIG. 2, endsat step 260.

Referring to FIG. 3, a method 300 of evaluating ammonia storage capacityof a close coupled SCR in accordance with a disclosed embodiment isillustrated. Method 300 starts at step 302. Step 304, is similar to step252 described above with reference to FIG. 2. Step 304 includesoperating an EAS connected to an internal combustion engine (includingat least a close-coupled SCR 112 and a downstream SCR 104) atsteady-state conditions. During operation of the EAS at steady-stateconditions, step 306 includes dosing diesel exhaust fluid from DEF doser114 into the exhaust gas from internal combustion engine that is flowingthrough the EAS. The diesel exhaust fluid is dosed into the exhaust gasupstream of the close coupled SCR 112. The exhaust gas, including thedosed DEF is received by the close coupled SCR 112 at step 308. At step310 exhaust gas from the close coupled SCR 112 flows to the downstreamSCR unit 104. In accordance with the disclosed embodiment of FIG. 3, atstep 312, emission of NOx from EAS is controlled by the downstream SCRcatalyst bed 104. Downstream SCR 104 controls NOx emissions to withinprescribed regulatory limits. At step 314, dosing of DEF into theexhaust gas upstream of the close-coupled SCR 112 is terminated ordeactivated. At step 316, EAS continues to operate after dosing of DEFhas terminated. As a result, ammonia stored in SCR 112 is depleted (viaNOx conversion). Depletion of the ammonia stored in close coupled SCR112 continues until it is determined that ammonia stored in closecoupled SCR 112 has been exhausted, for example, by determining closecoupled SCR 112 is no longer reducing the concentration of NOx in theexhaust gas entering SCR 112. In one embodiment, determining SCR 112 isno longer reducing the concentration of NOx in the exhaust gas enteringSCR 112 is detected by comparing the NOx concentration sensed by NOxsensor 116 b downstream of close coupled SCR 112 to the NOxconcentration sensed by NOx sensor 116 a, upstream of close coupled SCRunit 112. For example, when NOx sensor 116 b outputs a NOx concentrationequal to the NOx concentration output by NOx sensor 116 a, thisindicates SCR 112 is no longer converting NOx to desired products, e.g.,because ammonia within SCR 112 has been depleted.

At step 318, upon determining that ammonia stored in the close coupledSCR 112 has been exhausted, while continuing to operate under EAS,steady-state conditions, dosing of DEF from DEF doser 114 upstream ofclose coupled SCR 112 restarts. Upon restarting DEF dosing from DEFdoser 114, adsorption of ammonia within SCR 112 begins and NOxconversion within SCR 112 resumes. Referring to FIG. 7, the early stagesof this “adsorption phase” for SCR 112 is characterized by a decrease inthe signal generated by NOx sensor 116 b (as reflected by plot 702).Although plot 702 is labeled as NOx out, as described above, NOx sensors116 are unable to differentiate between NOx and ammonia; therefore, whenammonia is present in the exhaust gas that NOx sensors 116 areinterrogating, the signal generated by the NOx sensors 116 is anindication of concentration of NOx and ammonia in the exhaust gas. Whenthere is no ammonia present in the exhaust gas being interrogated bysensors 116, the signal generated by sensors 116 is an indication of theconcentration of NOx in the exhaust gas. The decrease in the signalgenerated by NOx sensor 116 b (referred to as NOx out of SCR 112 eventhough the signal may also represent ammonia out of SCR 112) in theearly stages of the absorption phase is also reflected as an increase indeNOx (e.g., ppm of NOx into SCR 112 minus ppm of NOx out of SCR 112.deNOx is the difference between NOx In and NOx Out of SCR 112 and at theright hand side of FIG. 7 is indicated by difference 704. As theduration of the adsorption phase increases, the amount of ammonia loadedin SCR 112 increases, and therefore the ammonia “missing” from SCR 112decreases as indicated by plot 706. The ability of a particular catalystto convert NOx varies depending on the temperature of substrate in theclose coupled SCR 112, the characteristics of the SCR catalyst itselfand the amount of DEF dosed into the exhaust gas to be treated. Theability of a particular SCR catalyst to convert NOx is determined bytesting the SCR catalyst under different conditions, e.g., catalysttemperature, NOx concentration, volumetric flow of exhaust gases and DEFdosing rates. From the results of this evaluation, a prediction can bemade of level of NOx converted to nitrogen and water (e.g., level ofdeNOx) provided by a particular catalyst operating at a particulartemperature. The deNOx achieved in close coupled SCR 112 can bepredicted by multiplying the amount of NOx converted by the SCR catalystas determined by the testing by the NOx concentration at the inlet ofthe close coupled SCR 112. From the values of NOx converted to nitrogenand water, whether based on actual measurements from NOx sensorsupstream and downstream of the SCR 112 or from a prediction based ontests results performed on the catalyst, an amount of ammonia consumedfor the amount of NOx converted (e.g., deNOx) can be calculated based onthe stoichiometry of the NOx conversion.

FIG. 7 also reflects a plot of baseline level of ammonia that isoxidized in close coupled SCR 112. The amount of ammonia oxidized inclose coupled SCR 112 is a function of substrate temperature withinclose coupled SCR 112 and the characteristics of the SCR catalyst withinclose coupled SCR 112. The amount of ammonia oxidized by the SCRcatalyst is determined by testing the SCR catalyst under differentconditions, e.g., catalyst temperature, NOx concentration, volumetricflow of exhaust gases and DEF dosing rates. The amount of ammoniaoxidized within close coupled SCR 112 is determined by multiplying theammonia concentration at the inlet to the close coupled SCR 112 by theamount of ammonia oxidized by the SCR catalyst as determined by thetesting.

In accordance with the embodiment of FIG. 3, reloading of close coupledSCR 112 continues at step 320 until a threshold ammonia loading of closecoupled SCR 112 is determined at step 322. In certain embodiments, athreshold ammonia loading is a maximum ammonia loading of close coupledSCR 112. A maximum ammonia loading of close coupled SCR 112 occurs whenammonia slip through close coupled SCR 112 begins. In the EAS embodimentof FIG. 2, such ammonia slip is indicated as an increase in the signaloutput by NOx sensor 116 b (reflecting an increase in NOx and ammoniaconcentration in the exhaust gas interrogated by sensor 116 b, which isunable to differentiate between NOx and ammonia). In FIG. 7, suchammonia slip is indicated by a change in the slope of the NOx out plot702. Embodiments in accordance with the present disclosure are notlimited to equating or determining the maximum ammonia loading of closecoupled SCR 112 as the point in time when a change in the slope of theNOx plot is determined. In accordance with other embodiments of thepresent disclosure, the maximum ammonia loading of close coupled SCR 112can be determined to occur when the other performance parameters of theclose coupled SCR 112 indicate that ammonia slip has started to occur.Examples of such other parameters include a reduction in deNOx % ofclose coupled SCR 112.

In accordance with the embodiment of FIG. 3, upon determining that theclose coupled SCR 112 has reached a maximum ammonia loading at step 322,method 300 includes step 324 which determines (1) the amount of ammonialoaded in the close coupled SCR 112 after restarting dosing of DEF intothe exhaust gas upstream of the close coupled SCR 112. Step 324 alsodetermines (2) an amount of ammonia used for NOx conversion in theclosed-coupled SCR 112 after restarting DEF dosing and (3) an amount ofammonia oxidized within close coupled SCR 112 after dosing of DEF fluidrestarted at step 318. At step 326, method 300 subtracts the amount ofammonia used for NOx conversion in the close coupled SCR 112 (2) and theamount of ammonia oxidized within close coupled SCR 112 after dosing ofDEF was restarted (3) from the amount of ammonia introduced to the closecoupled SCR 112 after restarting dosing of DEF into the exhaust gasupstream of the close coupled SCR 112 (1). The result of step 326 isevaluation of an amount of ammonia stored (e.g., the ammonia storagecapacity of the close coupled SCR 112) in the close coupled SCR 112.Method 300 ends at step 328.

The amount of ammonia introduced to the close coupled SCR 112 afterrestarting dosing of DEF into the exhaust gas upstream of the closecoupled SCR 112 (3) is determined based on the amount of DEF dosed intothe exhaust stream upstream of the close coupled SCR 112. The amount ofammonia oxidized within close coupled SCR 112 after dosing of DEFrestarted (3) is determined as described above. The amount of ammoniaused for NOx conversion in the close coupled SCR 112 after dosing of theDEF restarts (2) is determined as described above.

Referring to FIG. 4, a method 400 of controlling an emissionaftertreatment system (EAS) that includes two or more selectivecatalytic reduction units in accordance with embodiments of the presentdisclosure is illustrated. Method 400 starts at step 402 and includesstep 404 of evaluating ammonia storage capacity of a close coupled SCRwhile operating an EAS that includes the close coupled at steady stateconditions. EAS steady-state conditions have been described above, andwill not be repeated here in the interest of brevity. Evaluating ammoniastorage capacity of a close coupled SCR has been described above withreference to FIG. 3 and will not be described in more detail here in theinterest of brevity. In accordance with the embodiment of FIG. 4, atstep 406, during evaluation of ammonia storage capacity of the closecoupled SCR, NOx emissions from the internal combustion engine arecontrolled by the downstream SCR similar to the control of emissionsfrom the internal combustion engine described above with reference toFIGS. 2 and 3. At step 408, one or more operation parameters of the EASor internal combustion engine are adjusted based on the results of theevaluation of the ammonia storage capacity of the close coupled SCR.Examples of such one or more operation parameters of the EAS or internalcombustion engine include dosing rate of diesel exhaust fluid to anupstream SCR unit, dosing rate of diesel exhaust fluid to a downstreamSCR unit, temperature of the upstream SCR unit and temperature of thedownstream SCR unit, load on the internal combustion engine, temperatureof exhaust gas from the internal combustion engine and volumetric flowof air through the internal combustion engine, volumetric flow rate ofexhaust gases, volumetric flow of air to the engine, fuel/air ratio toengine, temperature of air flow to engine, NOx content of the exhaustgas from engine, NOx content of exhaust gas exiting an SCR unit,temperature of the engine, an operating speed of the internal combustionengine 102 (e.g., in RPM) and level of exhaust gas recirculation (EGR).Embodiments in accordance with the present disclosure are not limited tothe foregoing operational parameters. Operational parameters of theinternal combustion engine or the EAS in addition to those expresslylisted above can be adjusted in accordance with the present disclosure.

FIG. 5 illustrates a schematic diagram of a vehicle 101, which may be aheavy-duty vehicle, with an internal combustion engine 102, which may bea diesel engine, an exhaust after-treatment system 103, a set of atleast four wheels 106 configured to be powered and driven by the engine102, and a control system 110, which can perform the methods describedherein. When the vehicle 101 is in operation, the control system 110 canbe used to control operation of portions of the vehicle 101, includingits internal combustion engine 102 and its emission after-treatmentsystem 103. For example, the control system 110 may be configured tocontrol the engine 102 to idle with any number of its cylinders firingand any number of its cylinders deactivated, to control the engine 102to increase the load on the engine 102, for example by driving anelectric generator (not shown), to direct electrical energy generated bythe electrical generator into an exhaust gas stream at a locationbetween the engine 102 and the emission after-treatment system 103, toincrease or decrease the temperature of the gases exhausted from theengine and/or to increase or decrease the volumetric flow of air throughthe engine. These examples of functions the control system 110 is ableto control or initiate are not exhaustive. The control system 110 inaccordance with embodiments of the present disclosure may be able tocontrol or initiate other functions of the engine or vehicle. As anotherexample, the control system 110 may be configured to control the exhaustafter-treatment system 103 and components thereof, including a dieseloxidation catalyst (DOC) to oxidize unburned fuel and carbon monoxide, adiesel particulate filter (DPF) to control particulate matter (PM), aselective catalytic reduction (SCR) system to reduce oxides of nitrogen(NOX), and an ammonia oxidation catalyst (AMOX) system. For example, insome embodiments, the control system 110 is configured to control anamount of thermal energy introduced into the gas exhausted by theengine, to control the dosing rate of diesel exhaust fluid to the EASand/or to control temperature of an upstream or downstream SCR units.

In some embodiments, the vehicle 101 includes a plurality of sensorsthat collect and transmit data regarding operating parameters of thevehicle 101 and/or operating parameters of the EAS to the control system110, such as continuously. For example, such sensors may collect andtransmit data regarding an exhaust gas temperature, volumetric flow rateof exhaust gases, volumetric air flow rate to engine, fuel/air ratio toengine, temperature of air flow to engine, NOx content of the exhaustgas, NOx content of exhaust gas exiting the SCR units, volumetric flowof DEF dosing, temperature of the engine, an operating speed of theinternal combustion engine 102 (e.g., in RPM) to the control system 110,load on the engine, temperature of SCR unit and level of exhaust gasrecirculation (EGR). In some embodiments, the control system 110 maycontrol operation of the vehicle 101, such as in accordance with any ofthe techniques described herein, based on such measurements and data,such as when such measurements fall below certain specified thresholds,e.g., when the exhaust gas temperature falls below any of the exhaustgas temperatures mentioned herein, such as 190° C., or when the internalcombustion engine 102 is idling, as identified, for example, when theoperating speed of the internal combustion engine 102 falls below 550RPM, or 600 RPM, or 650 RPM, or 700 RPM, or 750 RPM, or 800 RPM. Othersensors may collect and transmit data regarding the EAS. For example,such sensors can collect and transmit data regarding NOx into anupstream SCR or into a downstream SCR, NOx out of an upstream SCR or outof a downstream SCR, quantity of DEF dosing and temperature of upstreamand/or downstream SCR.

FIG. 6 shows one non-limiting example of an emissions aftertreatmentsystem controller 148 formed in accordance with aspects of the presentdisclosure and can be part of the control system 110. The control systemmay be an emissions management system associated with an EAS system of avehicle powered by an internal combustion engine or an EAS of aninternal combustion engine implemented in a stationary application. Thecontroller 148 is connected in electrical communication with a pluralityof data sources 200 a-200 n (generally, data sources 200). As will bedescribed in more detail below, the data sources 200 may include but arenot limited to on-board sensors, e.g., engine sensors and EAS sensors,on-board state estimators, etc. It will be appreciated that thecontroller 148 can be connected directly (wired or wirelessly) to theplurality of data sources 200 or indirectly via any suitable interface,such as a CAN interface 202. Those skilled in the art and others willrecognize that the CAN 202 may be implemented using any number ofdifferent communication protocols such as, but not limited to, Societyof Automotive Engineers (“SAE”) J1587, SAE J1922, SAE J1939, SAE J1708,and combinations thereof. The controller 148 may also communicate withother electronic components of the vehicle 101 via the CAN 202 forcollecting data from other electronic components to be utilized by thecontroller 148, and as such, can also be considered in at least someembodiments as data sources 200. For example, the controller 148 mayreceive data from one or more other controllers 218, such as an enginecontroller, a transmission controller, a brake system controller, etc.In operation, as will be described in more detail below, the controller148 receives signals from the data sources 200, processes such signalsand others, and depending on the processed signals, transmits suitablecontrol signals for operating the EAS 150, the engine 103 or othersystems or components of the vehicle 101. The controller 148 initiatesoperation by means of a hard wired input (e.g. ignition key 154) or byreceiving a signal from a communication network (e.g. wake-up on CAN).This wake-up message allows to bring the controller 148 in operation,whereas the operator does not need to use the ignition keys or bephysically in or near the vehicle 101. The controller 148 may be astandalone controller or may be part of one or more other controllers(e.g., vehicle electronic control unit (VECU)) of the vehicle 101.Generally, the emission aftertreatment system may be implemented in anylocal or remote controller(s) operative to provide the functionalitydescribed herein.

In at least some embodiments, the controller 148 may contain logic rulesimplemented in a variety of combinations of hardware circuitrycomponents and programmed processors to effect control of the EAS 150and other systems of the vehicle 101. To that end, as furtherillustrated in FIG. 6, one suitable embodiment of the controller 148includes a nontransitory memory 204, a processor 206, and emissionsmanagement control module 208 for providing functionality of thecontroller 148. The memory 204 may include computer readable storagemedia in read-only memory (ROM) 210 and random-access memory (RAM) 212,for example. The computer-readable storage media may be implementedusing any of a number of memory devices such as PROMs (programmableread-only memory), EPROMs (electrically PROM), EEPROMs (electricallyerasable PROM), flash memory, or any other electric, magnetic, optical,or combination memory devices capable of storing data, including data214 (e.g., programmable parameters). The controller 148 also includesone or more input/output devices or components 216 that enable thecontroller to communicate with one or more local or remote devices viawired or wireless communication. In at least some embodiments, thecontroller 148 may include additional components including but notlimited to a high speed clock, analog to digital (A/D) and digital toanalog (D/A) circuitry, other input/output circuitry and devices (I/O),and appropriate signal conditioning and buffer circuitry.

As used herein, the term processor is not limited to integrated circuitsreferred to in the art as a computer, but broadly refers to one or moreof a microcontroller, a microcomputer, a microprocessor, a centralprocessing unit (CPU), a graphics processing unit (GPU), a programmablelogic controller, an application specific integrated circuit, otherprogrammable circuits, combinations of the above, among others. In atleast one embodiment, the processor 206 executes instructions stored inmemory 204, such as engine restart control module 208, to implement thefunctionality described in the present disclosure.

The emissions management control module 208 may include a set of controlalgorithms, including program instructions, selectable parameters, andcalibrations stored in one of the storage media and executed to providefunctions described herein. Information transfer to and from the module208 may be accomplished by way of a direct connection, a local areanetwork bus, a serial peripheral interface bus, wired or wirelessinterfaces, etc. The algorithms may be executed during preset loopcycles such that each algorithm is executed at least once each loopcycle. Algorithms stored in the non-volatile memory devices may beexecuted by the processor 206 to monitor inputs from the sensing devicesand other data transmitting devices or polls such devices for data to beused therein. Loop cycles may be executed at regular intervals duringongoing operation of the vehicle 101. Alternatively or additionally,algorithms may be executed in response to the occurrence of one or moreevents.

The processor 206 communicates with various data sources 200 directly orindirectly via the input/output (I/O) interface 216 and suitablecommunication links. The interface 216 may be implemented as a one ormore integrated interfaces that provide various raw data or signalconditioning, processing, and/or conversion, short-circuit protection,and/or the like. Additionally or alternatively, one or more dedicatedhardware or firmware chips may be used to condition and processparticular signals before being supplied to the processor 206. In atleast some embodiments, the signals transmitted from the interface 216may be suitable digital or analog signals.

The controller 148 may be a separate controller that implements the EASmanagement functionality described herein. However, it should beappreciated that the controller 148 may be a controller module, whichcould be software embedded within an existing on-board controller, suchas the engine controller, a general purpose controller, other vehiclesystem controllers, etc.

As briefly described above, the data sources 200 can include but are notlimited to on-board sensors for detecting operation parameters of anEAS, navigation/GPS devices, communications devices, data stores, remoteservers, etc. These data sources and others in at least some embodimentsmay be part of the electrical systems 138, control console 132, etc.,described above. The data supplied from these data sources 200 andothers may generally or specifically relate to vehicle operatingparameters, e.g., engine or EAS operating parameters, operator drivingtrends and accessories (e.g., loads 220) usage patterns andcharacteristics, and external parameters, including present vehiclenavigation, traffic patterns, weather data, sunrise and sunset data,temperature data, among others.

One or more implementations of the present disclosure are directed tosystems and methods for evaluating ammonia storage capacity of aselective catalytic reduction catalyst unit in an emissionaftertreatment system of an internal combustion engine, for example, adiesel engine of a light-duty or heavy-duty vehicle. In at least someimplementations, the systems and methods are operative to evaluateammonia storage capacity of a SCR unit intrusively during operation ofthe EAS and internal combustion engine while remaining in compliancewith existing emissions limits. The evaluation of ammonia storagecapacity of an SCR unit in accordance with disclosed embodiments areused, to control operation of the internal combustion engine, and/or theEAS so as to optimize the fuel efficiency of the intern engine and theefficiency NOx conversion by the EAS.

Although exemplary embodiments of the present disclosure are describedhereinafter with reference to a heavy duty truck, it will be appreciatedthat aspects of the present disclosure have wide application, andtherefore, may be suitable for use with many other types of vehicles,including but not limited to light and medium duty vehicles, passengervehicles, motor homes, buses, commercial vehicles, marine vessels,generator sets, etc. In addition, embodiments of the present disclosurehave application with internal combustion engines which are notassociated with vehicles. For example, embodiments of the presentdisclosure have application with internal combustion engines that areutilized in stationary applications, for example, power generation.Accordingly, the foregoing descriptions and illustrations herein shouldbe considered illustrative in nature, and thus, not limiting the scopeof the present disclosure.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A method of evaluating ammonia storage capacity of a selectivecatalytic reduction (SCR) unit in an emission aftertreatment system(EAS), the method comprising: operating the EAS at steady stateconditions; dosing diesel exhaust fluid, into exhaust gas from theinternal combustion engine, upstream of a close-coupled SCR unit;flowing the exhaust gas, into which the diesel exhaust fluid has beendosed, through the close-coupled SCR unit; flowing the exhaust gas fromthe close-coupled SCR unit through a downstream SCR unit; controllingNOx emissions from the EAS using the downstream SCR unit; terminatingthe dosing of diesel exhaust fluid into the flowing exhaust gas upstreamof the close-coupled SCR unit; depleting ammonia stored in theclose-coupled SCR unit; restarting the dosing of diesel exhaust fluidinto the flowing exhaust gas upstream of the close-coupled SCR unit;reloading the close-coupled SCR unit with ammonia; determining theclose-coupled SCR unit has reached a maximum ammonia loading; and upondetermining the close-coupled SCR unit has reached the threshold ammonialoading, determine (1) an amount of ammonia loaded in the close-coupledSCR unit after restarting dosing of diesel exhaust fluid into theflowing exhaust gas upstream of the close-coupled SCR unit, (2) anamount of ammonia used for NOx conversion in the close-coupled SCR unitafter restarting dosing of diesel exhaust fluid into the flowing exhaustgas close-coupled of the close-coupled SCR unit and (3) an amount ofammonia oxidized in the SCR unit after restarting dosing of dieselexhaust fluid into the flowing exhaust gas upstream of the close-coupledSCR unit; and evaluating an amount of ammonia stored in theclose-coupled SCR unit by subtracting (2) and (3) from (1).
 2. Themethod of claim 1, wherein the steady-state conditions includetemperature of the close-coupled SCR unit being substantially constant.3. The method of claim 2, wherein the steady-state conditions furtherincludes volumetric flow of exhaust gas being substantially constant. 4.The method of claim 3, wherein the steady-state conditions furtherinclude, NOx content of the exhaust gas upstream of the close-coupledSCR unit being substantially constant.
 5. The method of claim 1, whereinthe downstream SCR unit controls NOx emissions from the EAS during thedepleting ammonia stored in the close-coupled SCR unit.
 6. The method ofclaim 1, wherein the determining the close-coupled SCR unit has reacheda maximum ammonia loading further comprises: evaluating an output of theclose-coupled SCR unit using a NOx sensor downstream of theclose-coupled SCR unit; determining that a signal output by the NOxsensor representing a level of NOx in the output of the close-coupledSCR unit has increased.
 7. The method of claim 1, further comprisingincreasing an amount of diesel exhaust fluid dosed to the downstream SCRunit.
 8. The method of claim 1, wherein the determining theclose-coupled SCR unit has reached a maximum ammonia loading furthercomprises determining ammonia slip from the close-coupled SCR unit hasbegun.
 9. The method of claim 6, wherein the determining that a signaloutput by the NOx sensor representing a level of NOx in the output ofthe close-coupled SCR unit has increased further comprises, for theclose-coupled SCR unit, determining a % reduction in NOx content of theexhaust gas into the close-coupled SCR unit has decreased.
 10. A methodof operating an emission aftertreatment system (EAS) that includes twoor more selective catalytic reduction (SCR) catalyst units and isconnected to an internal combustion engine, the method comprising:evaluating ammonia storage capacity of a close-coupled SCR unit whileoperating the EAS at steady state conditions; during the evaluatingammonia storage capacity of an close-coupled SCR unit, controlling NOxemissions from the EAS using a downstream SCR unit; and adjusting one ormore operation parameters of the EAS based on the result of theevaluating ammonia storage capacity of an close-coupled SCR unit. 11.The method of claim 10, wherein the evaluating ammonia storage capacityof a close-coupled SCR unit further comprises: operating the EAS atsteady state conditions; dosing diesel exhaust fluid, into exhaust gasfrom the internal combustion engine, upstream of an close-coupled SCRunit; flowing the exhaust gas, into which the diesel exhaust fluid hasbeen dosed, through the close-coupled SCR unit; flowing the exhaust gasfrom the close-coupled SCR unit through a downstream SCR unit;terminating the dosing of diesel exhaust fluid into the flowing exhaustgas upstream of the close-coupled SCR unit; depleting ammonia stored inthe close-coupled SCR unit; restarting the dosing of diesel exhaustfluid into the flowing exhaust gas upstream of the close-coupled SCRunit; reloading the close-coupled SCR unit with ammonia; determining theclose-coupled SCR unit has reached a threshold ammonia loading; and upondetermining the close-coupled SCR unit has reached the threshold ammonialoading, determine (1) an amount of ammonia loaded in the close-coupledSCR unit after restarting dosing of diesel exhaust fluid into theflowing exhaust gas upstream of the close-coupled SCR unit, (2) anamount of ammonia used for NOx conversion in the close-coupled SCR unitafter restarting dosing of diesel exhaust fluid into the flowing exhaustgas upstream of the close-coupled SCR unit and (3) an amount of ammoniaoxidized in the SCR unit after restarting dosing of diesel exhaust fluidinto the flowing exhaust gas upstream of the close-coupled SCR unit; andevaluating an amount of ammonia stored in the close-coupled SCR unit bysubtracting (2) and (3) from (1).
 12. The method of claim 10, furthercomprising adjusting one or more operation parameters of the internalcombustion engine connected to the EAS based on the result of theevaluating ammonia storage capacity of an close-coupled SCR unit. 13.The method of claim 10, wherein the one or more operation parameters ofthe EAS is selected from dosing rate of diesel exhaust fluid to anclose-coupled SCR unit, dosing rate of diesel exhaust fluid to adownstream SCR unit, temperature of the close-coupled SCR unit andtemperature of the downstream SCR unit.
 14. The method of claim 12,wherein the one or more operation parameters of the internal combustionengine connected to the EAS is selected from load on the internalcombustion engine, temperature of exhaust gas from the internalcombustion engine, volumetric flow of exhaust gas, volumetric flow ofair through the internal combustion engine, temperature of air flow tothe engine and fuel to air mixture for the internal combustion engine.15. The method of claim 14, wherein the load on the internal combustionengine is adjusted by driving an electric generator with the internalcombustion engine and/or deactivating a cylinder of the internalcombustion engine.
 16. The method of claim 14, wherein the temperatureof the exhaust gas is adjusted by exhaust gas recirculation or addingthermal energy to the exhaust gas.
 17. The method of claim 14, whereinthe volumetric flow of air is adjusted by deactivating one or morecylinders of the internal combustion engine and/or reducing idling speedof the internal combustion engine.
 18. An emission management system fora vehicle including an internal combustion engine and an emissionaftertreatment system (EAS) that includes a close-coupled SCR unit and adownstream SCR unit, the emission management system comprising: at leastone nontransitory processor-readable storage medium that stores one ofprocessor-executable instructions or data; at least one processorcommunicatively coupled to the at least one nontransitoryprocessor-readable storage medium, in operation, the at least oneprocessor: receives an indication of an ammonia storage capacity of aclose-coupled SCR unit determined while operating the EAS at steadystate conditions; stores the received indication of an ammonia storagecapacity of a close-coupled SCR unit determined while the EAS operatesat steady state conditions in the nontransitory processor-readablestorage medium; and controls the operation of the internal combustionengine and/or the EAS, using the received indication of ammonia storagecapacity, to control emissions from the EAS to within prescribed limits.19. The emission management system of claim 18, wherein the at least oneprocessor initiates an adjustment of one or more of dosing rate ofdiesel exhaust fluid to the close-coupled SCR unit, dosing rate ofdiesel exhaust fluid to the downstream SCR unit, temperature of theclose-coupled SCR unit and temperature of the downstream SCR unit. 20.The emission management system of claim 18, wherein the at least oneprocessor initiates an adjustment of load on the internal combustionengine, temperature of exhaust gas from the internal combustion engine,volumetric flow of exhaust gas, volumetric flow of air through theinternal combustion engine, temperature of air flow to the engine andfuel to air mixture for the internal combustion engine.